1. Field of the Invention
The invention generally relates to heart rate monitors for use in association with exercising equipment. In particular, the invention relates to a two electrode monitor employing digital signal processing of signals detected by the electrodes.
2. Description of the Prior Art
Heart rate monitors for use with road bikes and other exercise equipment are known in the art. In general, such monitors tend to require four electrodes, two for each hand, in-order to accurately detect a beat to beat heart rate. Some patented prior art monitors include the following. U.S. Pat. No. 3,702,113 illustrates a heart rate monitor with only one electrode per hand. U.S. Pat. No. 5,243,993 discloses a heart rate monitor which includes a digital signal processor 44 for implementing autocorrelator 26, signal processor 28 and arbitrator 30. Similarly, Antii Ruha, Sami Sallinen and Seppo Nissilxc3xa4, in A Real-Time Microprocessor ORS Detector System with a 1-ms Timing Accuracy for the Measurement of Ambulatory HRV, IEEE Transactions on Biomedical Engineering, March 1997, teach the use of digital signal processing in connection with monitoring a patient""s heart rate.
U.S. Pat. No. 5,337,753 is directed to a four-electrode (two electrodes per hand) heart rate monitor. Specifically, it calls for a first live electrode and a first common electrode mounted on one half of an elongate member in spaced relationship with each other and a second live electrode and a second common electrode mounted on the other half of the elongate member in spaced relationship with each other.
Referring next to U.S. Pat. No. 5,337,753, it discloses an apparatus for measuring heart rate having at least the following features: (i) sensor means for generating an input signal including the biopotential signal produced by the user""s heart, (ii) autocorrelating means responsive to the input signal for periodically generating an autocorrelation signal of the input signal over a predetermined time period and, (iii) signal indication means responsive to the autocorrelation signal for detecting the presence of at least one periodic signal in the autocorrelation signal and generating a heart rate signal corresponding to the detected signal (s).
U.S. Pat. No. 4,319,581 describes an apparatus having a first hand grip for attachment to one end of the handlebar of a bicycle or stationary exercise device, a second hand grip including a second means for electrically contacting the other end of said handlebar, third and fourth means disposed upon said second hand grip in spaced apart relationship and adapted to electrically engage said other hand of said user, and signal monitoring means for measuring electric pulses created in the body and for indicating the heart pulse rate of such body.
There is a need for a low cost, accurate monitor which digitally processes signals on a power spectrum basis rather than a peak to peak basis, which employs only two electrodes and which includes an isolation barrier.
It is therefore an object of this invention to provide a low cost heart rate monitor which employs only two electrodes.
It is a further object of this invention to provide an accurate heart rate monitor which may be used in combination with road bikes and other exercise equipment.
It is also an object of this invention to provide a heart rate monitor which through digital signal processing based on the power spectrum provides heart rate information which is reliable.
The invention meets these needs and objects in at least three ways. First, the invention provides only one electrode per hand which avoids the problem of sweat accumulation between electrodes. Second, the invention uses an isolation barrier which allows the monitor to meet Underwriter Laboratories"" and other safety specifications. Third, the invention uses digital signal processing to calculate the power spectrum, namely the application of discrete Fourier transforms with Goertzel""s algorithm, to substantially reduces noise from motion artifacts, especially when the user is exercising rigorously, so that an accurate beat rate can be detected.
In one form, the invention-comprises a heart rate monitor for use with road bikes and other exercise equipment to calculate the user""s heart rate while exercising. The monitor includes first and second electrodes and a signal processor. The first electrode is disposed at a first location on the road bikes and other exercise equipment for contacting the user and for sensing the user""s heart rate. The first electrode produces a first sensed signal representative of the user""s heart rate. The second electrode is disposed at a second location on the road bikes and other exercise equipment for contacting the user and for sensing the user""s heart rate. The second electrode produces a second sensed signal representative of the user""s heart rate. The signal processor produces a difference signal indicative of a difference between the first and second sensed signals. The signal processor further includes a power spectrum analyzer calculating the user""s heart rate by measuring the power spectrum of the difference signal and producing a processed heart rate signal as a function of the measured power spectrum whereby the processed heart rate signal is indicative of the heart rate of the user as sensed by the first and second electrodes.
In another form, the invention comprises a heart rate monitor for use with road bikes and other exercise equipment to calculate the user""s heart rate while exercising having only two electrodes and a signal processor.
In another form, the invention comprises an exercise apparatus comprising an exercise device for exercising the user and a heart rate monitor such as noted above for use with road bikes and other exercise equipment to calculate the user""s heart rate while exercising.
The invention also includes a method of monitoring the heart rate of a person comprising the steps of:
contacting the person with a first electrode for sensing the person""s heart rate, the first electrode producing a first sensed signal representative of the person""s heart rate;
contacting the person with a second electrode for sensing the person""s heart rate, the second electrode producing a second sensed signal representative of the person""s heart rate;
producing a difference signal indicative of a difference between the first and second sensed signals;
measuring the power spectrum of the difference signal; and
producing a processed heart rate signal as a function of the measured power spectrum whereby the processed heart rate signal is indicative of the heart rate of the person as sensed by the first and second electrodes.
Other objects and features will be in part apparent and in part pointed out hereinafter.